Air drilling method using controlled split stream

ABSTRACT

Method and apparatus for drilling and for obtaining uncontaminated formation samples with an air hammer by flowing compressed air down through the tubing annulus of a dual pupe string to a novel sub, where the flow divides to enable part of the air to power the air hammer while the remaining air flow is directed into the hole annulus. The spent air exhausts from the bit face and carries cuttings back into the sub and into the inner tubing string. An enlargement formed on the sub exterior prevents comingling of the samples with material from the borehole annulus.

United States Patent Elenburg [54] AIR DRILLING METHOD USING CONTROLLED SPLIT STREAM [72] Inventor: Wayland D. Elenburg, P. O. Box 1588, Monahans, Tex. 79756 [22] Filed: May 11, 1970 21 App1.No.: 36,352

VIIIAI'IIIIIIIII 1 June 6,1972

3,155,179 11/1964 l-luntetal ..l75/2l5 3,534,822 10/1970 Campbell ..175/205X Primary Examiner-David H. Brown Attorney-Marcus L. Bates [57] ABSTRACT Method and apparatus for drilling and for obtaining uncontaminated formation samples with an air hammer by flowing compressed air down through the tubing annulus of a dual pupe string to a novel sub, where the flow divides to enable part of the air to power the air hammer while the remaining air flow is directed into the hole annulus. The spent air exhausts from the bit face and carries cuttings back into the sub and into the inner tubing string. An enlargement formed on the sub exterior prevents comingling of the samples with material from the borehole annulus.

10 Claims, 10 Drawing Figures PATENTEDJUH 61972 @isl 'NJ 20 U 21 22 5 23 i. 1 i 11 I l l sum 1 UF 2 i fi 19 i5 2 r w 23 3 L i N VE N TOR. WAYLAND D. ELENBURC MARCUS L. BA 5 H/S 465 N VENTOZ WAYLAND D. ELENBURG BY MARCUS LBATES SHEET 2 BF 2 m m H J PATENTEUJUH s 1912 H/S HGENT AIR DRILLING METHOD USING CONTROLLED SPLIT STREAM BACKGROUND OF THE INVENTION The use of an air hammer to actuate a bit when forming boreholes is known to those skilled in the art. The air hammer is especially adapted for hard drilling, that is, penetrating rock and the like. Often when drilling a well with conventional equipment and a hard formation is encountered, it has been found expedient to change to an air hammer so as to be able to penetrate the hard formation. However, operation of an air hammer becomes impractical when an aquifer is encountered because the hydrostatic head which developes above the air hammer soon necessitates application of an air pressure of a magnitude which exceeds the normal capacity of compressors commonly associated with drilling rigs. Some drillers have found that the presence of as much as a three to five gallon per minute water flow can be tolerated, but any excess over this amount causes difficulty and the air hammer operation must accordingly be discontinued.

When obtaining formation samples by the air drilling process, formation bits and pieces resulting from the previously drilled borehole continue to contaminate the sample as it is being circulated up from the drill bit because of the abrasive action of the sample particles as they travel up the borehole annulus; or, because particles from the borehole sidewall continue to fall downhole and become admixed with cuttings from the bit.

When sinking a borehole and a void or cavity is encountered, circulation is usually lost because the drilling fluid flows into the void following the path of least resistance, thereby causing loss of formation samples.

It is a common practice to employ an air hammer and force all of the cuttings from the bit to flow uphole, however, this expedient causes the chips to blast or erode the sidewall and contaminate the samples. Moreover, this action breaks the samples up into undesirably small particles. If an aquifer is encountered during this type drilling process, the increase of the hydrostatic head soon precludes continuation of the drilling operation. Furthermore, when friable formations are encountered, the air drilling process produces unsatisfactory samples because of contamination brought about by particles becoming dislodged from the upper wall and falling to the bottom of the borehole. Those more advanced in the art have found it advantageous to employ a concentrically arranged string of pipe, that is, a dual pipe string, so as to reduce contamination of a sample with the debris from uphole. However, it has been found that such a method permits debris to be pulled into the return fluid stream, thereby still causing a substantial amount of sample contamination to occur.

In the chip drilling process wherein a dual string is used, with air traveling down the drill pipe annulus to the drill bit where sample particles are picked up and returned through the inner string, it would be desirable to be able to prevent uphole debris from contaminating the samples as they are being formed by the action of the bit at the bottom of the hole. It would also be desirable to avoid pumping water back up through the central string when an aquifer is encountered. Moreover, it would be desirable to be able to continue sampling a formation when a void is encountered. Most importantly, it would especially be desirable to be able to actually continue the air drilling process under dry drilling conditions after the bit has passed through an aquifer.

SUMMARY OF THE INVENTION The present invention sets forth a new method for drilling with an air hammer by the provision of a split stream of drilling fluid in conjunction with a dual pipe string, wherein compressed air is conducted downhole within the drill string annulus to a drill bit sub where the flow divides into two separate paths; with one path being flow connectedto the borehole annulus so as to keep formation particles located therein suspended and moved in an upward direction while the remaining flow path continues on to an air hammer which actuates a drill bit located at the lower free end thereof. The spent air from the hammer cools and cleans the bit and returns the immediate cuttings to a flow passageway located within the sub. Form the sub this last flow passageway continues to the inner tubing of the drill string where the formation samples are carried to the surface of the earth for suitable packaging and subsequent analysis.

It is therefore an object of the present invention to provide uncontaminated samples which are transported from a drill bit back to the surface of the earth without being admixed with other formation particles.

Another object of this invention is to enable an air drilling process to be carried out in conjunction with an air hammer where water flooding is encountered.

A still further object of this invention is the provision of an air drilling method which has one stream of air used to power an air drill and to return samples to the surface of the earth while another stream of air is conducted upwardly through the borehole annulus so as to fluidize debris contained therein.

A still further object of the present invention is the provision of a method of drilling with an air hammer wherein fractures located within various formations do not cause the continual loss of samples.

Still another object of the present invention is the provision of a method of drilling which assures the geologist that any particular sample undergoing analysis absolutely was obtained from a specified depth within the borehole.

These and other objects of the present invention are made possible by both method and apparatus as set forth in the above summary and abstract.

Various other objects and advantages of this invention will become readily apparent to those skilled in the art upon reading the following detailed description and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross-sectional view of a borehole which has been formed within the earth, and with apparatus disposed therein which has been made in accordance with the present invention, so as to provide a better comprehension of the present method,

FIG. 2 is an enlarged cross-sectional view of a portion of the apparatus seen in FIG. 1, and which enables the practice of the present invention when used in conjunction with a conventional air drilling rig;

FIGS. 3, 4, 5, and 6 respectively, are cross-sectional views taken along line 3-3, 44, 55, and 6-6, respectively, of FIG. 2;

FIG. 7 is an enlarged, longitudinal, cross-sectional view of an alternate embodiment of a sub which is similar to the one disclosed in FIGS. 2-6.

FIGS. 8 and 9, respectively, are cross-sectional views taken along line 8-8 and 9-9, respectively, of FIG. 7, and

FIG. 10 is a diagrammatical, part cross-sectional view of still another embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS Throughout the various figures of the drawing, wherever possible, like or similar numerals refer to like or similar parts.

As seen in FIG. 1, in conjunction with FIGS. 2-6, a crosssection of the upper crust of the earth 10 has been penetrated by earth boring apparatus having a drill string 1 l to form borehole 12. The borehole extends through an aquifer 14, and spaced perhaps several hundred feet therefrom, although it could be adjacent thereto, is seen a cavity or void 15 which is in communication with the borehole. Included within the drill string is schematically illustrated an air hammer 16 which can be of any suitable design. Preferably the air hammer is of the reciprocatory or vibratory type which drives a rock bit 17. The

and chips away cuttings and samples therefrom.

The drill string includes a drill pipe 18 which is attached to the sub at 19' with the sub being attached to the air hammer as seen at 19". Inner tubing 20 is spaced apart from the inside peripheral surface 21 of the drill pipe so as to form a drill pipe annulus 22 and an inner tubing passageway 23. Hence it is seen that three concentrically arranged flow passageways, the hole annulus at 12, the drill pipe annulus 22, and the inner tubing passageway 23, exist and cooperate with the apparatus used in practicing the present method.

Formed in drill bit sub 19 are a series of radially spaced apart upwardly directed ports 24, each of which is flow connected to a source of air pressure while the lowermost portion of the bit at 25 includes the usual exhaust ports which are likewise indirectly connected to the same source of air pressure as ports 24 so as to cause fluid flowing through the drill pipe annulus at 22 to be split into the two described flow paths. Radially spaced apart inlets, one of which is seen at 26, are formed within a ramada 27 so as to form an inlet for cuttings and air which constitutes the return flow from the lower extremity of the bit. The term ramada is intended to mean the tunnel-like configuration of the lower skirt portion 29 of the sub, which offers the least resistance to flow from the bit face. Drilled passageway 30 communicates with inlet 26 and the inner tubing by means of the outwardly depending tubular portions 31 which provides the internal passageways 32 and 33. Hence the tubular portions form a cross-over" for return fluid from the bit.

Looking now to the details of the embodiment seen in FIGS. 7-9, those skilled in the art will realize that one of the differences in the embodiments of FIGS. 2 and 7 lies in the provision of three radially spaced apart inlets, 126 and 127, which are also vertically staggered from one another so as to provide a sub having greater structural integrity as compared to the sub of FIG. 2. As seen in FIG. 7, ramada 127 extends upwardly to the upper most portion of passageway 132, for example, so as to enable fluid to enter the unobstructed lower portion of the ramada which is formed by skirt 141 so as to enhance fluid flow from the bit face back up and into the return passageways. Inner tubing 120 is plugged at 129 and is provided with the spaced apart tubular pup-joints" 131 which communicate each of the return passageways with the inner tubing and which provides a cross-over for the two isolated fluid streams. Passageway 140 provides a source of air pressure to the air hammer which is attached to the lower depending end of the sub at 116'.

Several pieces of flat stock material 142 are radially spaced apart from one another and welded between the inside peripheral wall surface of the sub and the outer peripheral wall surface of the inner tubing connector. The upper marginal end portions 143, 144 of the sub and inner tubing connection are preferably fabricated in a manner illustrated and described in Henderson, US. Pat. No. 3,208,539, with particular emphasis being directed to FIGS. 2A, 6, and 7 thereof.

Looking now to the details of FIG. 10, the embodiment generally indicated by the arrow at numeral 1 l 1 includes a sub having a drill bit 117 attached at the lower extremity thereof. The drill bit 117 preferably is fabricated in accordance with FIG. 4 of my previous US. Pat. No. 3,439,757. As illustrated, compressed fluid is circulated down drill pipe annulus 222 with a portion of the fluid exhausting through radial ports 224 and the remainder of the fluid flowing through orifice 250 and under weir 248 and into close proximity to the cones 249 whereupon the fluid transports the cuttings obtained back up under each of the ramadas 227 and into inlets 226, where the cuttings along with the fluid return through the inner tubing 220 to the surface of the earth.

OPERATION In operation, the drill string is rotated 4 to 8 revolutions per minute so as to avoid boring a crooked hole, while air is pumped down the drill pipe annulus passageway 22 where the flow splits within the sub at annulus 28. About half of the air flow is directed through radial ports 24 and the remainder of the split air stream flows about the cross-over and to the removable orifice located within the intake of the air hammer. The action of the compressed air flowing through the motor of the hammer causes the bit to reciprocate, thereby forming the borehole.

The compressed air exhausts from the lower bit surface and carries formation cuttings up the lower borehole annulus and into the ramada. The air along with the cuttings enters each of the return inlets, flows through passageways 32, 33 of the cross-over, up through the inner tubing passageway 23 and on to the surface of the earth where the samples may be suitably stored. It should be noted that the outer peripheral surface 119 of the drill bit sub enlargement is equal to the outside diameter of the drill bit 17 so as to maintain close tolerance between the enlargement and the inside peripheral wall surface of the borehole. This close tolerance offers resistance to the passage of air which would otherwise tend to flow across the enlargement and into proximity of ports 24.

The remaining portion of the split stream exits at ports 24 and flows back up the hole annulus and to the surface of the ground, thereby preventing debris which would otherwise fall downhole from being admixed with the samples being obtained at drill bit face 25. The close tolerance of the enlargement together with the action of the air exiting at ports 24 maintains the loose particles in the hole annulus in a fluidized state as the flow continues up the borehole. The enlargement and air pressure exiting at ports 24 isolate the loose particles in the upper borehole annulus from the particles which flow into the ramadas.

Assuming that an aquifer is encountered by the bit, water will be produced only while the bit is penetrating the stratum within which the aquifer is located, after which the ports at 24, together with the action of the enlargement, will effectively isolate the water bearing stratum from the formation being penetrated by the drill bit. This is one of the major teachings of this invention. In other words, once the enlargement has passed the aquifer, the radially spaced apart ports effectively provide an air lift so as to commence lifting water within the borehole annulus to the surface of the earth. This method of air lifting the liquid permits the bit to continue to penetrate the dry formation which otherwise would be under water, thereby causing an unfavorable drilling condition which usually leads to discontinued use of the air hammer.

Assuming a fissure or void is encountered, such as seen at 15, particles will be lost into the void only for a limited time which is determined by the depth of the void. As the bit continues to penetrate the earth, enlargement 19 will again engage the borehole annulus immediately below the void and effectively seal the void from the drill bit. As the enlargement passes the bottom of the void, circulation back up through the inner tubing will be regained. As the drilling continues, subsequent contamination of the sample from the debris lost at 15 is precluded by this method of drilling.

In the embodiment of FIG. 7, compressed air flows down the tubing annulus and splits into two different flow paths, one exiting through the radial passageways. The remaining portion of the stream continues across the passageways 131, 132 and through passageway where it flows on to the motor of the air hammer, as in the before described embodiment. The staggered relationship of the return passageways 131, 132 increases the strength of the sub for the reason that the crosssectional area of the sub is increased. As seen in FIG. 8, it is preferred to plug alternate radial passageways at 124' so as to enable adjustment to be made between the air flow through the ports as compared to the air flow through the air hammer. These passageways are plugged with babbitt which easily can be drilled out as required in order to properly balance the two split streams. Moreover, the air hammer is provided with an orifice at the inlet thereof which can be changed as desired so as to regulate the total volume of air flowing into the air hammer. Furthermore, the external peripheral surface 119 of the enlargement is made of mild or soft steel or any other metal which will cause its wear rate to be equivalent to the wear rate of the outside diameter of the bit, thereby maintaining a close tolerance between the outer surface of the enlargement and the inside surface of the borehole. For this reason it is desirable to change to a new sub when the drill bit is renewed. The old sub is easily resurfaced.

As a specific example of the apparatus used in carrying out the present method of drilling, the sub of FIG. 7 is attached to an air hammer identified as a 4210 Mission Hammer," fabricated by Mission Manufacturing Company of Houston, Texas. The outside diameter of the hammer is equivalent to the outside diameter of the bit and the upper end of the sub is attached to a drill string which is 4 inchs o.d with a 3 1% inch bore at 122; and, an enlargement which is 5 7/32 inch o.d. by l 1 inches in length, with the total length of the sub being 24 inches. Six drilled passageways 3/16 inch id and three radially disposed return fluid inlet conduits 1 34 inch i.d. Drilling fluid in the form of compressed air is forced into annulus 122 at a rate of 600 c.f.m. at 125 p.s.i. with the flow splitting so as to enable 300 c.f.m. to exit through the radial ports while the remainder of the flow continues to the air hammer. This rate of flow provides a velocity of approximately 3,000 f.p.m./lO c.f.m. up the hole annulus and 3,600 f.p.m./l00 c.f.m. up the inner tubing.

It is obvious that any cuttings obtained uphole from the central tubing must have been obtained from the drill bit, and accordingly, the sample can be precisely indexed with respect to the specific depth of the borehole. Highly fractured mineral deposits can be accurately sampled by using the method of the present invention. As various conditions are encountered the radial ports may be either plugged or unplugged along with changing the orifice in the air hammer so as to properly split the flow of drilling fluid to the sub.

I claim:

1. In an earth boring operation wherein there is provided a dual pipe string, with the dual pipes being concentrically arranged to provide a central flow passageway and a drill string annulus, passageway and with a formation cutting bit being supported by the lower end of the pipe string, and wherein the pipe string is adapted to cooperate with the borehole to form a borehole annulus, the method of forming a borehole comprising the steps of:

l. flowing drilling fluid through the drill string annulus passageway downhole towards the formation cutting bit; splitting the flow of drilling fluid of step (1) into two different flow paths prior to the drilling fluid reaching the bit;

3. connecting one flow path of step (2) to the bit so as to remove cuttings from the bottom of the borehole as they are formed by the bit;

. flowing the cuttings and drilling fluid of step (3) a limited distance up the borehole annulus, into the central passageway where the cuttings continue to flow uphole to the surface of the ground;

. connecting the remaining flow path of step (2) to the borehole annulus at a location above the flow path described in step (4) so as to preclude contamination of the cuttings of step (4) with other formation particles remaining in the borehole annulus;

6. maintaining the flow paths set forth in steps (1), (4), and

(5) separated from one another.

2. The method of claim 1 and further including the step of interposing a flow obstruction between the flow paths set forth in steps (4) and (5) so as to maintain the two flow paths essentially separated from each other.

3. The method of claim 1 and further including the steps of:

7. interposing an air hammer between the drill string and bit; and,

8. using the flow path of step (3) to actuate an air hammer,

and using the air hammer to power the bit, prior to connecting the air flow of step (3) to the bit.

4. The method of claim 1 wherein an air hammer is connected between the drill pipe string and the drill bit, and using the flow path of step (3) to provide power for the air hammer,

with the spent drilling fluid from the air hammer being used in carrying out step (4).

5. The method of claim 1, and further including forming an enlargement within the borehole annulus at a location between the flow path set forth in step (5) and the flow path set forth in step (4) so as to provide a flow restriction therebetween which prevents the two flow paths from mixing together.

6. The method of claim 1, wherein the drilling fluid of step (l) is air, and further including the step of connecting an air hammer between the bit and the end of the pipe string; and, using the flow path of step (3) for actuating the air hammer; and, using the spent power fluid from the air hammer as the fluid medium of step (4).

7. The method of forming boreholes by the following steps:

I flow conducting drilling fluid downhole to a bit sub;

2. connecting a formation cutting bit to the bit sub by a fluid actuated motor which powers the bit;

3. flowing part of the drilling fluid from the bit sub into the hole annulus and up the hole annulus towards the surface of the ground;

4. flowing another part of the drilling fluid from the bit sub to the fluid actuated motor to cause the motor to actuate the bit;

5. flowing the spent drilling fluid from the fluid actuated motor to the bit so as to remove cuttings therefrom;

6. flowing the spent drilling fluid and cuttings obtained in step (5) from the bit, up a limited length of the borehole annulus, and back into the sub at a location spaced apart from and below the flow path of step (3 7. interposing an enlargement within the borehole annulus and between the spaced apart flow paths of step (6);

8. flowing the spent drilling fluid and cuttings of step (6) from the sub and uphole to the surface of the ground;

9. maintaining the flow paths of steps (I), (3), and (8 separate from each other by providing three concentrically arranged flow paths which are isolated from one another.

8. The method of claim 7 and further including the step of using air as the drilling fluid; and, using an air hammer as the fluid actuated motor.

9. The method of claim 7 wherein the fluid actuated motor is an air hammer; and further including: i

10. using compressed air as the drilling fluid.

10. The method of claim 7, and further including the step of locating the fluid actuated motor below the sub; and flow conducting the spent fluid from the motor through a cross-over meanslocated in the sub, so that the flowing material of steps (1) and (8) flow countercurrent along the recited concentric flow paths. 

1. In an earth boring operation wherein there is provided a dual pipe string, with the dual pipes being concentrically arranged to provide a central flow passageway and a drill string annulus, passageway and with a formation cutting bit being supported by the lower end of the pipe string, and wherein the pipe string is adaptEd to cooperate with the borehole to form a borehole annulus, the method of forming a borehole comprising the steps of:
 1. flowing drilling fluid through the drill string annulus passageway downhole towards the formation cutting bit;
 2. splitting the flow of drilling fluid of step (1) into two different flow paths prior to the drilling fluid reaching the bit;
 3. connecting one flow path of step (2) to the bit so as to remove cuttings from the bottom of the borehole as they are formed by the bit;
 4. flowing the cuttings and drilling fluid of step (3) a limited distance up the borehole annulus, into the central passageway where the cuttings continue to flow uphole to the surface of the ground;
 5. connecting the remaining flow path of step (2) to the borehole annulus at a location above the flow path described in step (4) so as to preclude contamination of the cuttings of step (4) with other formation particles remaining in the borehole annulus;
 6. maintaining the flow paths set forth in steps (1), (4), and (5) separated from one another.
 2. splitting the flow of drilling fluid of step (1) into two different flow paths prior to the drilling fluid reaching the bit;
 2. The method of claim 1 and further including the step of interposing a flow obstruction between the flow paths set forth in steps (4) and (5) so as to maintain the two flow paths essentially separated from each other.
 2. connecting a formation cutting bit to the bit sub by a fluid actuated motor which powers the bit;
 3. flowing part of the drilling fluid from the bit sub into the hole annulus and up the hole annulus towards the surface of the ground;
 3. The method of claim 1 and further including the steps of:
 3. connecting one flow path of step (2) to the bit so as to remove cuttings from the bottom of the borehole as they are formed by the bit;
 4. flowing the cuttings and drilling fluid of step (3) a limited distance up the borehole annulus, into the central passageway where the cuttings continue to flow uphole to the surface of the ground;
 4. flowing another part of the drilling fluid from the bit sub to the fluid actuated motor to cause the motor to actuate the bit;
 4. The method of claim 1 wherein an air hammer is connected between the drill pipe string and the drill bit, and using the flow path of step (3) to provide power for the air hammer, with the spent drilling fluid from the air hammer being used in carrying out step (4).
 5. The method of claim 1, and further including forming an enlargement within the borehole annulus at a location between the flow path set forth in step (5) and the flow path set forth in step (4) so as to provide a flow restriction therebetween which prevents the two flow paths from mixing together.
 5. flowing the spent drilling fluid from the fluid actuated motor to the bit so as to remove cuttings therefrom;
 5. connecting the remaining flow path of step (2) to the borehole annulus at a location above the flow path described in step (4) so as to preclude contamination of the cuttings of step (4) with other formation particles remaining in the borehole annulus;
 6. maintaining the flow paths set forth in steps (1), (4), and (5) separated from one another.
 6. flowing the spent drilling fluid and cuttings obtained in step (5) from the bit, up a limited length of the borehole annulus, and back into the sub at a location spaced apart from and below the flow path of step (3);
 6. The method of claim 1, wherein the drilling fluid of step (1) is air, and further including the step of connecting an air hammer between the bit and the end of the pipe string; and, using the flow path of step (3) for actuating the air hammer; and, using the spent power fluid from the air hammer as the fluid medium of step (4).
 7. The method of forming boreholes by the following steps:
 7. interposing an enlargement within the borehole annulus and between the spaced apart flow paths of step (6);
 7. interposing an air hammer between the drill string and bit; and,
 8. using the flow path of step (3) to actuate an air hammer, and using the air hammer to power the bit, prior to connecting the air flow of step (3) to the bit.
 8. flowing the spent drilling fluid and cuttings of step (6) from the sub and uphole to the surface of the ground;
 8. The method of claim 7 and further including the step of using air as the drilling fluid; and, using an air hammer as the fluid actuated motor.
 9. The method of claim 7 wherein the fluid actuated motor is an air hammer; and further including:
 9. maintaining the flow paths of steps (1), (3), and (8 ) separate from each other by providing three concentrically arranged flow paths which are isolated from one another.
 10. using compressed air as the drilling fluid.
 10. The method of claim 7, and further including the step of locating the fluid actuated motor below the sub; and flow conducting the spent fluid from the motor through a cross-over means located in the sub, so that the flowing material of steps (1) and (8) flow countercurrent along the recited concentric flow paths. 